Commercially available solar regulators generally operate using one of two basic methods or a combination of these methods. One method is the employment of a series regulator which uses a varying resistance in series with the charge current flow. The resistance is varied as a function of battery voltage such that the charge current is restricted or tapered off gradually to a trickle charge rate when the batteries are fully charged.
The second method is the shunt regulator principle where a variable resistance is paralleled to the batteries such that as the voltage of the batteries increases, the shunting resistance is caused to decrease, shunting current away from the battery. The resultant is again a tapering charge applied to the batteries.
The series-parallel regulator applies both principles simultaneously, resulting in the same resultant action.
The prime disadvantage to all of these methods is that a nominal impedance exists in all of the regulators connected between the solar modules and the storage battery. This results in an unacceptable energy loss even when regulation is neither occurring nor required.
Another disadvantage is that the amount of current regulated or controlled is limited by the heat dissipating ability of the current carrying components of the conventional regulators, typically requiring the installation of additional regulators as the system is expanded.